CN115428329A

CN115428329A - Elastic wave device and ladder filter

Info

Publication number: CN115428329A
Application number: CN202180029585.8A
Authority: CN
Inventors: 木村哲也; 野竹直弘
Original assignee: Murata Manufacturing Co Ltd
Current assignee: Murata Manufacturing Co Ltd
Priority date: 2020-04-29
Filing date: 2021-04-28
Publication date: 2022-12-02
Anticipated expiration: 2041-04-28
Also published as: CN115428329B; WO2021222433A1; US20230053722A1; CN117254781A

Abstract

The purpose is as follows: provided is an elastic wave device including a cavity portion, in which a piezoelectric film is less likely to break. The solution is as follows: an elastic wave device (1) includes a piezoelectric film (2) made of lithium niobate or lithium tantalate, and first electrode fingers (3) and second electrode fingers (4) facing each other in a direction intersecting with a thickness direction of the piezoelectric film (2). When the average thickness of the piezoelectric film (2) is d and the distance between the centers of the first electrode fingers (3) and the second electrode fingers (4) is p, d/p is about 0.5 or less. The first electrode finger (3) and the second electrode finger (4) are connected to a first busbar (5) and a second busbar (6), respectively. The first busbar (5) and the second busbar (6) comprise corners. At least one of the corner portions (5 e) to (5 h) and (6 e) to (6 h) of the first busbar (5) and the second busbar (6) is outside the cavity portion (9) when viewed in a plan view.

Description

Elastic wave device and ladder filter

Cross Reference to Related Applications

This application claims priority to U.S. patent application No.63/017,101 filed on 29/4/2020. The entire contents of this application are incorporated herein by reference.

Technical Field

The present invention relates to an elastic wave device including a cavity portion below a piezoelectric film and a ladder filter including the elastic wave device.

Background

Conventionally, an elastic wave device in which a cavity portion is provided below a piezoelectric film is known. For example, patent document 1 listed below discloses an elastic wave device using Lamb waves (Lamb waves) as plate waves. In this elastic wave device, a cavity portion is provided in a support substrate. The piezoelectric film overlaps the cavity portion. The IDT electrode is disposed on an upper surface of the piezoelectric film. Reflectors are provided on both sides of the IDT electrode. Thus, an elastic wave resonator using a plate wave is constructed.

[ Prior art documents ]

[ patent document ]

[ patent document 1] Japanese patent application laid-open No.2012-257019

Disclosure of Invention

[ problem to be solved by the invention ]

In the elastic wave device including the cavity portion described in patent document 1, the piezoelectric film may be broken.

Preferred embodiments of the present invention provide an elastic wave device including a cavity portion but reducing or preventing a piezoelectric film from breaking, and a ladder filter including such an elastic wave device.

[ means for solving problems ]

According to a preferred embodiment of the present invention, an elastic wave device includes: a support substrate including a first main surface and a recess opening to the first main surface; a piezoelectric film made of lithium niobate or lithium tantalate laminated on the first main surface of the support substrate and defining a cavity portion together with the recess and the support substrate; and an electrode on the piezoelectric film and including a first bus bar and a second bus bar, a first electrode finger connected to the first bus bar, and a second electrode finger connected to the second bus bar; wherein the first busbar and the second busbar comprise a plurality of corners when viewed in plan; the elastic wave device uses a bulk wave of a thickness slip mode; and at least one of the corners of the first and second busbars is outside the cavity when viewed in plan.

According to a preferred embodiment of the present invention, an elastic wave device includes: a support substrate including a first main surface and a recess opening to the first main surface; a piezoelectric film made of lithium niobate or lithium tantalate laminated on the first main surface of the support substrate and defining a cavity portion together with the recess and the support substrate; and an electrode on the piezoelectric film, and includes a first bus bar and a second bus bar, a first electrode finger connected to the first bus bar, and a second electrode finger connected to the second bus bar; wherein the first busbar and the second busbar comprise a plurality of corners when viewed in plan; when the thickness of the piezoelectric film is d and the distance between the centers of the first electrode fingers and the second electrode fingers is p, d/p is about 0.5 or less; and at least one of the corners of the first and second busbars is outside the cavity when viewed in plan.

According to a preferred embodiment of the present invention, an elastic wave device includes: a support substrate including a first main surface and a recess opening to the first main surface; a piezoelectric film laminated on the first main surface of the support substrate and defining a cavity portion together with the recess and the support substrate; and an IDT electrode on the piezoelectric film such that a portion of the IDT electrode overlaps the cavity portion, wherein the IDT electrode includes a first bus bar and a second bus bar, a plurality of first electrode fingers connected to the first bus bar, and a plurality of second electrode fingers connected to the second bus bar, the plurality of first electrode fingers and the plurality of second electrode fingers are interleaved with each other, the first bus bar and the second bus bar include a plurality of corner portions when viewed in plan view, and at least one of the corner portions of the first bus bar and the second bus bar is outside the cavity portion when viewed in plan view.

[ Effect of the invention ]

According to preferred embodiments of the present invention, it is possible to provide an elastic wave device that includes a cavity portion but reduces or prevents breakage of a piezoelectric film, and a ladder filter including such an elastic wave device.

The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments with reference to the attached drawings.

Drawings

Fig. 1A and 1B are a perspective view and a plan view for explaining an elastic wave device according to a first preferred embodiment of the present invention.

Fig. 2 isbase:Sub>A sectional view showingbase:Sub>A portion of an elastic wave device according tobase:Sub>A first preferred embodiment of the present invention, taken along linebase:Sub>A-base:Sub>A of fig. 1A.

Fig. 3A is a schematic front cross-sectional view for explaining a lamb wave propagating in a piezoelectric film of a conventional elastic wave device, and fig. 3B is a schematic front cross-sectional view for explaining a bulk wave of a thickness slip mode propagating in the piezoelectric film in the elastic wave device according to the first preferred embodiment of the present invention.

Fig. 4 is a diagram showing the amplitude direction of a bulk wave in the thickness slip mode.

Fig. 5 is a graph showing the relationship between d/2p and a specific frequency band as a resonator when the distance between the centers of adjacent electrodes or the average distance of the distances between the centers of adjacent electrodes is p and the thickness of the piezoelectric film is d.

Fig. 6 is a partially cut-away top view for explaining a problem of the conventional elastic wave device.

Fig. 7A and 7B are a perspective view and a plan view for explaining an elastic wave device according to a second preferred embodiment of the present invention.

Fig. 8 is a sectional view of a portion of an elastic wave device according to a second preferred embodiment of the present invention, taken along line B-B of fig. 7A.

Fig. 9 is a plan view for explaining an elastic wave device according to a third preferred embodiment of the present invention.

Fig. 10 is a plan view for explaining an elastic wave device according to a fourth preferred embodiment of the present invention.

Fig. 11 is a front sectional view for explaining an elastic wave device according to a fifth preferred embodiment of the present invention.

Fig. 12 is a plan view for explaining an elastic wave device according to a sixth preferred embodiment of the present invention.

Fig. 13 is a top view of a composite filter device including a ladder filter as a seventh preferred embodiment of the present invention.

Fig. 14 is a circuit diagram of the composite filter device shown in fig. 13.

Fig. 15 is a partially cut-away perspective view for explaining an elastic wave device according to an eighth preferred embodiment of the present invention.

Fig. 16 is a schematic top view of an elastic wave device according to an eighth preferred embodiment of the present invention.

Fig. 17 is a schematic plan view for explaining a main portion of an elastic wave device according to a ninth preferred embodiment of the present invention.

Fig. 18 is a front sectional view for explaining an elastic wave device according to a tenth preferred embodiment of the present invention.

Fig. 19 is a front sectional view for explaining an elastic wave device according to an eleventh preferred embodiment of the present invention.

Detailed Description

Hereinafter, the present invention will be explained by explaining preferred embodiments of the present invention with reference to the accompanying drawings.

It should be noted that each of the preferred embodiments described herein is exemplary, and partial substitutions or configuration combinations may be made between different preferred embodiments.

(first preferred embodiment)

The first preferred embodiment of the present invention includes a piezoelectric film made of lithium niobate or lithium tantalate, and first and second electrode fingers. The piezoelectric film includes a first main surface and a second main surface facing each other, and the first electrode fingers and the second electrode fingers are disposed on the first main surface.

In the first preferred embodiment, a thickness slip mode (thickness slip mode) bulk wave is used. Further, in the second preferred embodiment of the present invention, when the average thickness of the piezoelectric film is d and the distance between the centers of the first and second electrode fingers is p, d/p is about 0.5 or less. Therefore, in the first preferred embodiment and the second preferred embodiment, the Q value can be increased even if the size of the elastic wave device is reduced.

Fig. 1A isbase:Sub>A perspective view of an elastic wave device for explainingbase:Sub>A first preferred embodiment of the present invention, fig. 1B isbase:Sub>A plan view showing an electrode structure onbase:Sub>A piezoelectric film, and fig. 2 isbase:Sub>A sectional view showingbase:Sub>A portion taken along linebase:Sub>A-base:Sub>A in fig. 1A.

For example, the elastic wave device 1 includes a material preferably made of LiNbO ₃ The piezoelectric film 2 is produced. For example, the piezoelectric film 2 may be formed of LiTaO ₃ And (4) preparing. LiNbO ₃ Or LiTaO ₃ The cutting angle of (b) is Z-cut in the preferred embodiment, but may be a rotational Y-cut or X-cut. For example, propagation directions of Y propagation and X propagation ± about 30 ° are preferred. The thickness of the piezoelectric film 2 is not particularly limited, but is, for example, preferably about 50nm or more and about 600nm or less to efficiently excite the thickness slip mode.

The piezoelectric film 2 includes a first main surface 2a and a second main surface 2b facing each other. The first electrode fingers 3 and the second electrode fingers 4 are disposed on the first main surface 2 a. In fig. 1A and 1B, a plurality of first electrode fingers 3 are connected to a first bus bar 5. The plurality of second electrode fingers 4 are connected to a second bus bar 6. The plurality of first electrode fingers 3 and the plurality of second electrode fingers 4 are interleaved with each other. The first electrode fingers 3 and the second electrode fingers 4 have a rectangular or substantially rectangular shape and have a length direction. The first electrode fingers 3 and the adjacent second electrode fingers 4 face each other in a direction orthogonal or substantially orthogonal to the longitudinal direction. Both the longitudinal directions of the first electrode fingers 3 and the second electrode fingers 4 and the direction orthogonal or substantially orthogonal to the longitudinal directions of the first electrode fingers 3 and the second electrode fingers 4 are directions intersecting the thickness direction of the piezoelectric film 2. Therefore, the first electrode fingers 3 and the adjacent second electrode fingers 4 face each other in a direction intersecting the thickness direction of the piezoelectric film 2. In addition, the longitudinal direction of the first electrode fingers 3 and the second electrode fingers 4 may be switched to a direction orthogonal or substantially orthogonal to the longitudinal direction of the first electrode fingers 3 and the second electrode fingers 4 shown in fig. 1A and 1B. That is, in fig. 1A and 1B, the first electrode fingers 3 and the second electrode fingers 4 may extend in a direction in which the first bus bar 5 and the second bus bar 6 extend.

In this case, the first bus bar 5 and the second bus bar 6 extend in the direction in which the first electrode fingers 3 and the second electrode fingers 4 extend in fig. 1A and 1B. A plurality of pairs of electrode fingers in which the first electrode finger 3 connected to one potential and the second electrode finger 4 connected to another potential are adjacent to each other are provided in a direction orthogonal or substantially orthogonal to the length direction of the first electrode finger 3 and the second electrode finger 4.

Here, the state in which the first electrode fingers 3 and the second electrode fingers 4 are adjacent to each other does not refer to the case in which the first electrode fingers 3 and the second electrode fingers 4 are arranged to be in direct contact with each other, but refers to the case in which the first electrode fingers 3 and the second electrode fingers 4 are arranged to be spaced apart from each other. Further, when the first electrode fingers 3 and the second electrode fingers 4 are adjacent to each other, an electrode connected to a hot electrode or a ground electrode including the other first electrode fingers 3 and second electrode fingers 4 is not disposed between the first electrode fingers 3 and the second electrode fingers 4. The logarithm need not be an integer pair but may be, for example, 1.5 pairs, 2.5 pairs, etc.

For example, the distance (i.e., pitch) between the centers of the first and

second electrode fingers

3 and 4 is preferably in the range of about 1 μm or more and about 10 μm or less. The distance between the centers of the first electrode finger 3 and the second electrode finger 4 is a distance connecting the center of the width dimension of the first electrode finger 3 in the direction orthogonal or substantially orthogonal to the longitudinal direction of the first electrode finger 3 and the center of the width dimension of the second electrode finger 4 in the direction orthogonal or substantially orthogonal to the longitudinal direction of the second electrode finger 4.

Further, in the case where at least one of the first electrode fingers 3 and the second electrode fingers 4 is provided in plurality (1.5 or more pairs of electrodes are provided when the first electrode fingers 3 and the second electrode fingers 4 are regarded as electrode pairs), the distance between the centers of the first electrode fingers 3 and the second electrode fingers 4 means an average value of respective distances between the centers of adjacent first electrode fingers 3 and second electrode fingers 4 among the 1.5 or more pairs of first electrode fingers 3 and second electrode fingers 4. Further, for example, the widths of the first and second electrode fingers 3 and 4 (i.e., the dimensions of the first and

second electrode fingers

3 and 4 in the facing direction) are preferably in the range of about 150nm or more and about 1,000nm or less.

Further, in the present preferred embodiment, since the piezoelectric film is cut using Z, the direction orthogonal or substantially orthogonal to the length direction of the first electrode fingers 3 and the second electrode fingers 4 is a direction orthogonal or substantially orthogonal to the polarization direction of the piezoelectric film 2. This does not apply to the case where a piezoelectric material having another cut angle is used as the piezoelectric film 2. Here, "orthogonal" is not limited to the case of being strictly orthogonal, but may be substantially orthogonal (the direction orthogonal to the longitudinal direction of the first electrode fingers 3 and the second electrode fingers 4 makes an angle of, for example, about 90 ° ± 10 ° with the polarization direction PZ 1).

The support member 8 is laminated on the second main surface 2b side of the piezoelectric film 2 via the insulating layer 7. The support substrate is a laminated body including the support member 8 and the insulating layer 7. Therefore, the main surface of the insulating layer 7 on the piezoelectric film 2 side is the first main surface of the support substrate. The insulating layer 7 and the support member 8 have a frame shape, and include opening

portions

7a and 8a as shown in fig. 2. Thus, the cavity portion 9 is provided. The cavity portion 9 does not interfere with the vibration of the excitation region of the piezoelectric film 2. Therefore, the support member 8 is laminated on the second main surface 2b via the insulating layer 7 at a position not overlapping with a portion where at least one pair of the first electrode finger 3 and the second electrode finger 4 is provided. The insulating layer 7 may not be provided. Thus, the support member 8 may be directly or indirectly laminated on the second main surface 2b of the piezoelectric film 2.

For example, the insulating layer 7 is preferably made of silicon oxide. However, in addition to silicon oxide, a suitable insulating material, such as silicon oxynitride or aluminum oxide, may be used. For example, the support member 8 is preferably made of Si. The plane orientation on the Si surface on the piezoelectric film 2 side may be (100) or (111). Preferably, high resistance Si having a resistivity of, for example, about 2k Ω or more is used. However, the support member 8 may also be configured by using an appropriate insulating material or semiconductor material, for example.

The plurality of first and

second electrode fingers

3 and 4 and the first and

second bus bars

5 and 6 are made of a suitable metal or alloy (e.g., al or AlCu alloy). In the present preferred embodiment, for example, the first and

second electrode fingers

3 and 4 and the first and

second bus bars

5 and 6 have a structure in which an Al film is laminated on a Ti film.

A close contact layer other than the Ti film may be used.

In the elastic wave device 1, vibration in a thickness slip mode described later is excited as an elastic wave by applying an AC voltage between the first electrode fingers 3 and the second electrode fingers 4. In order not to disturb such vibration, a cavity portion 9 is provided below the piezoelectric film 2.

However, in the elastic wave device including the cavity portion, the corner portions of the first bus bar and the second bus bar may be located inside the cavity portion in a plan view. In this case, pressure concentrates on the piezoelectric film at the corner, and cracking may occur. This will be described with reference to fig. 6.

In the IDT electrode 110, one end of a first electrode finger 113 and one end of a second electrode finger 114 are connected to a first bus bar 111 and a second bus bar 112, respectively. The IDT electrode 110 is disposed on the piezoelectric film 115, and the cavity portion is disposed below the piezoelectric film 115. The dotted line B in fig. 6 shows the peripheral edge of the cavity when viewed in plan. Here, the first bus bar 111 and the second bus bar 112 include a plurality of corner portions (portions where external lines of the bus bars intersect with each other at ends of the bus bars in a plan view) surrounded by circles X1 and X2. In other words, the first busbar 111 and the second busbar 112 each include one or more corners, such that the first busbar 111 and the second busbar 112 generally include a plurality of corners. These corners are located inside the cavity when viewed in plan.

Meanwhile, the first bus bar 111 and the second bus bar 112 are physically coupled to the support substrate via the piezoelectric film 115. However, if the corner portions of the first bus bar 111 and the second bus bar 112 are disposed above the cavity portion, a large pressure is applied to the piezoelectric film 115 side at the corner portions, and the piezoelectric film 115 may be broken.

In the elastic wave device 1 according to the first preferred embodiment, in order to prevent cracking, at least one corner portion of the first bus bar 5 and the 2 nd bus bar 6 is located outside the cavity portion 9 as viewed in plan.

More specifically, the first bus bar 5 and the second bus bar 6 have a rectangular or substantially rectangular shape and have a length direction. The longitudinal direction is a direction orthogonal or substantially orthogonal to the longitudinal direction of the first electrode finger 3 and the second electrode finger 4, and is an elastic wave propagation direction.

The first bus bar 5 includes

long sides

5a and 5b extending in the lengthwise direction and

short sides

5c and 5d extending in a direction orthogonal or substantially orthogonal to the

long sides

5a and 5 b. Similarly, the second bus bar 6 includes

long sides

6a and 6b and

short sides

6c and 6d.

Thus, the first busbar 5 and the second busbar 6 include corner portions 5e to 5h and 6e to 6h, respectively.

Here, the corner portion refers to a portion where two straight sides adjoin and the vicinity thereof. Specifically, the corner portions may refer to

corner portions

5f, 5h, 6f, and 6h on a side of the respective first and

second bus bars

5 and 6 connecting the first and

second electrode fingers

3 and 4.

In fig. 1B, the outer edge of the cavity 9 is shown by a dashed line. The first busbar 5 and the second busbar 6 having a lengthwise direction are provided to extend to an outer region of the cavity 9 in the lengthwise direction. The corner portions 5e to 5h and 6e to 6h are located outside the cavity portion 9 in plan view.

Therefore, since the corners 5e to 5h and 6e to 6h, at which the stress on the piezoelectric film 2 increases, are located outside the cavity portion 9, the piezoelectric film 2 is less likely to be broken.

In the elastic wave device 1, for example, in the first bus bar 5, all of the corners 5e to 5h are located outside the cavity 9 as viewed in plan, but it is only necessary that at least one corner be located outside the cavity 9. This is because the stress concentration at the corner located outside the cavity 9 can be relaxed.

However, it is preferable that all of the corners 5e to 5h are located outside the cavity 9.

Further, in the acoustic wave device 1, the long side 5b of the first bus bar 5 is located inside the cavity 9, and the long side 5a is located outside the cavity 9. Therefore, it is preferable that the

corner portions

5f and 5h at both ends of the long side 5b inside the cavity 9 are located outside the cavity 9. In this case, the remaining

corner portions

5e and 5g are located outside the cavity portion 9.

When the elastic wave device 1 is driven, an AC voltage is applied between the plurality of first electrode fingers 3 and the plurality of second electrode fingers 4. More specifically, an AC voltage is applied between the first bus bar 5 and the second bus bar 6. Therefore, the bulk wave of the thickness slip mode excited in the piezoelectric film 2 can be used to obtain the resonance characteristic. Further, in the elastic wave device 1, for example, when the average thickness of the piezoelectric film 2 is d and the distance between the centers of the adjacent first electrode fingers 3 and second electrode fingers 4 of any one of the pairs of first electrode fingers 3 and second electrode fingers 4 is p, d/p is preferably about 0.5 or less. Therefore, the bulk wave of the thickness slip mode is excited efficiently, and good resonance characteristics can be obtained. More preferably, d/p is about 0.24 or less, and in this case, better resonance characteristics can be obtained. In the case where at least one of the first electrode fingers 3 and the second electrode fingers 4 is provided in plurality as in the present preferred embodiment (i.e., when the first electrode fingers 3 and the second electrode fingers 4 are electrode pairs, 1.5 or more pairs of the first electrode fingers 3 and the second electrode fingers 4 are provided), the distance p between the centers of the adjacent first electrode fingers 3 and second electrode fingers 4 refers to the average distance of the distances between the centers of the adjacent first electrode fingers 3 and second electrode fingers 4.

Since the elastic wave device 1 of the present preferred embodiment has the above-described configuration, the Q value is not easily lowered even if the number of pairs of the first electrode fingers 3 and the second electrode fingers 4 is reduced in order to reduce the size. This is because the elastic wave device 1 is a resonator which does not require reflectors on both sides and has a small propagation loss. Further, the reason why the above-described reflector is not required is that a thickness slip mode bulk wave is used. The difference between a lamb wave and a bulk wave of a thickness slip mode used in a conventional elastic wave device will be described with reference to fig. 3A and 3B.

Fig. 3A is a schematic front cross-sectional view for explaining a lamb wave propagating in a piezoelectric film of an elastic wave device described in patent document 1. Here, the wave propagates in the piezoelectric film 201 as indicated by an arrow. Here, in the piezoelectric film 201, the first main surface 201a and the second main surface 201b face each other, and a thickness direction connecting the first main surface 201a and the second main surface 201b is a Z direction. The X direction is a direction in which electrode fingers of the IDT electrode are aligned. In lamb waves, as shown in FIG. 3A, the wave propagates in the X direction as shown. The wave is a plate wave. Therefore, although the piezoelectric film 201 vibrates as a whole, the wave propagates in the X direction, and thus reflectors are provided on both sides to obtain resonance characteristics. Therefore, a propagation loss of the wave occurs, and when the size is reduced (i.e., the number of pairs of electrode fingers is reduced), the Q value is lowered.

On the other hand, as shown in fig. 3B, in the elastic wave device of the present preferred embodiment, a vibration displacement is generated in the thickness slip direction, so that a wave propagates and resonates in the direction connecting the first main surface 2a and the second main surface 2B of the piezoelectric film 2 (i.e., in the Z direction) or substantially in the Z direction. That is, the X-direction component of the wave is significantly smaller than the Z-direction component. Since the resonance characteristic is obtained by the propagation of the wave in the Z direction, no reflector is required. Therefore, there is no propagation loss when the wave propagates to the reflector. Therefore, even if the number of pairs of electrodes including first electrode fingers 3 and second electrode fingers 4 is reduced in order to reduce the size of the elastic wave device, the Q value is not easily lowered.

As shown in fig. 4, between the first region 451 included in the excitation region of the piezoelectric film 2 and the second region 452 included in the excitation region, the amplitude directions of the bulk waves of the thickness slip mode are opposite.

In fig. 4, a bulk wave when a voltage that causes the second electrode fingers 4 to have a higher potential than the first electrode fingers 3 is applied between the first electrode fingers 3 and the second electrode fingers 4 is schematically shown. The first region 451 is in an excitation region between an imaginary plane VP1 and the first main surface 2a, the imaginary plane VP1 being orthogonal or substantially orthogonal to the thickness direction of the piezoelectric film 2 and dividing the piezoelectric film 2 into two. The second region 452 is in the excitation region between the imaginary plane VP1 and the second major surface 2b.

As described above, in the elastic wave device 1, at least one pair of electrodes including the first electrode finger 3 and the second electrode finger 4 is provided, but the wave does not propagate in the X direction. Therefore, the number of pairs of electrodes including the first electrode fingers 3 and the second electrode fingers 4 is not necessarily a plurality of pairs. That is, at least one pair of electrodes may be provided.

For example, the first electrode finger 3 is connected to a thermal potential, and the second electrode finger 4 is connected to a ground potential. However, the first electrode fingers 3 may be connected to a ground potential and the second electrode fingers 4 may be connected to a thermal potential. In the present preferred embodiment, as described above, at least one pair of electrodes is an electrode connected to a thermoelectric potential and an electrode connected to a ground potential, and a floating electrode is not provided.

Incidentally, when the average thickness of the piezoelectric film 2 is d and the distance between the centers of the electrodes of the first electrode fingers 3 and the second electrode fingers 4 is p, as described above, in the present preferred embodiment, for example, d/p is preferably about 0.5 or less, and more preferably about 0.24 or less. This will be described with reference to fig. 5.

However, similarly to the elastic wave device in which the above resonance characteristics were obtained, d/2p was changed, and a plurality of elastic wave devices were obtained. Fig. 5 is a diagram showing a relationship between d/2p of the elastic wave device and a specific frequency band as a resonator.

As is clear from FIG. 5, when d/2p exceeds about 0.25, i.e., when d/p > about 0.5, the specific frequency band is less than about 5% even if d/p is adjusted. On the other hand, when d/2p is ≦ about 0.25, i.e., when d/p is ≦ about 0.5, by changing d/p within this range, the specific frequency band may be set to about 5% or more, i.e., a resonator having a high coupling coefficient may be obtained. Further, when d/2p is about 0.12 or less, that is, when d/p is about 0.24 or less, the specific frequency band may be increased to about 7% or more. In addition, if d/p is adjusted within this range, a resonator having a wider specific frequency band can be obtained, and a resonator having a higher coupling coefficient can be obtained. It can be seen therefore that by setting d/p to about 0.5 or less as in the second preferred embodiment of the present invention, a bulk wave of thickness slip mode can be used to construct a resonator having a high coupling coefficient.

As described above, at least one pair of electrodes may be a pair, and in the case of a pair of electrodes, p is a distance between centers of adjacent first and

second electrode fingers

3 and 4. In the case of 1.5 or more pairs of electrodes, the average distance of the distances between the centers of the adjacent first and

second electrode fingers

3 and 4 may be p.

Further, as for the average thickness d of the piezoelectric film, when the piezoelectric film 2 has thickness variation, a value obtained by averaging the thicknesses may be employed.

(second preferred embodiment)

Fig. 7A and 7B are a perspective view and a top view for explaining an elastic wave device according to a second preferred embodiment of the present invention, and fig. 8 is a sectional view of a portion taken along line B-B of fig. 7B.

In the elastic wave device 21, the second-

layer electrode patterns

23 and 24 are provided on the piezoelectric film 2. Further, the first bus bar 5 and the second bus bar 6 are disposed such that the outer long sides extend to the outer sides of the second-

layer electrode patterns

23 and 24. The elastic wave device 21 is configured in the same or substantially the same manner as the elastic wave device 1 except for the planar shapes of the first and

second bus bars

5 and 6 and the second-

layer electrode patterns

23 and 24.

Preferably, the second-

layer electrode patterns

23 and 24 are made of, for example, a metal material having higher conductivity than the first bus bar 5 and the second bus bar 6. Therefore, the resistance can be reduced, and the loss can be reduced.

In the present preferred embodiment, the second-

layer electrode patterns

23 and 24 may be provided to cover a part or all of the first bus bar 5 and the second bus bar 6 in this manner.

Also in this case, the corner portions of the first bus bar 5 and the second bus bar 6 are located outside the cavity portion 9 when viewed in plan view. Therefore, also in the elastic wave device 21 according to the second preferred embodiment, the piezoelectric film 2 above the cavity section 9 is less likely to be broken.

(third preferred embodiment)

Fig. 9 is a plan view for explaining an elastic wave device according to a third preferred embodiment of the present invention. In the elastic wave device 31, the

corners

5f, 5h, 6f, and 6h in the first bus bar 5 and the second bus bar 6 are rounded. That is, the

corner portions

5f, 5h, 6f, and 6h are curved. Therefore, the stress concentration of the piezoelectric film 2 at the

corner portions

5f, 5h, 6f, and 6h can be reduced. Therefore, the breakage of the piezoelectric film 2 at the

corner portions

5f, 5h, 6f, and 6h can be further reduced or prevented.

Also in the elastic wave device 31, all the corners are located outside the cavity portion 9 when viewed in plan view. Therefore, the breakage of the piezoelectric film 2 at all the corners can be reduced.

(fourth preferred embodiment)

In the elastic wave device 41 according to the fourth preferred embodiment, of the corner portions of the first bus bar 5 and the second bus bar 6, the corner portions of the

short sides

5c, 5d, 6c, and 6d abutting the

long sides

5b and 6b are cut away, and the outer peripheral edges are configured as oblique sides 5i, 5j, 6i, and 6j. In this way, by cutting off the corners and providing the oblique sides 5i, 5j, 6i, 6j, the stress concentration of the piezoelectric film 2 at the corners can be reduced.

Also in the elastic wave device 41, all the corners are located outside the cavity portion 9 when viewed in plan view. Therefore, as in the first to third preferred embodiments, the piezoelectric film is less likely to be broken at each corner.

(fifth preferred embodiment)

Fig. 11 is a front sectional view for explaining an elastic wave device according to a fifth preferred embodiment of the present invention. In the elastic wave device 51, the protective film 52 covers the first electrode fingers 3 and the second electrode fingers 4. Such a protective film 52 may be provided. Therefore, the moisture resistance can be improved.

Further, the frequency-temperature characteristics can be adjusted by using, for example, silicon oxide or the like as the protective film 52. As the material of the protective film 52 as described above, various insulators such as silicon oxide, silicon oxynitride, silicon nitride, and the like can be used.

(sixth preferred embodiment)

Fig. 12 is a top view of an elastic wave device according to a sixth preferred embodiment of the present invention. In the elastic wave device 61, a pair of electrodes including the first electrode fingers 3 and the second electrode fingers 4 is provided on the first main surface 2a of the piezoelectric film 2. In addition, K in FIG. 12 is the length of the excitation region. As described above, in the elastic wave device of the present preferred embodiment, the number of pairs of electrodes may be one pair. Even in this case, if d/p is about 0.5 or less, bulk waves of thickness slip mode can be excited efficiently.

(seventh preferred embodiment)

Fig. 13 is a plan view of a composite filter device 71 including a ladder filter as a seventh preferred embodiment of the present invention, and fig. 14 is a circuit diagram thereof.

For example, the composite filter device 71 is used for an RF stage of a smartphone or the like. The composite filter device 71 includes a piezoelectric film 72. Below the piezoelectric film 72, a support substrate including a plurality of concave portions defining or serving as cavity portions is bonded.

The common terminal 73 is provided on the piezoelectric film 72. The common terminal 73 is connected to an antenna. The ladder filter 75 and the vertical coupling resonator filter 77 are connected between the common terminal 73 and the reception terminal 74. The ladder filter 75 includes series-arm resonators S1 and S2 and parallel-arm resonators P1 and P2 defined by elastic wave resonators. For example, the elastic wave device 1 may be used as at least one of the series-arm resonators S1 and S2 and the parallel-arm resonators P1 and P2 of the ladder filter 75.

Further, a transmission filter including a ladder filter is disposed between the common terminal 73 and the transmission terminal 79. The transmission filter includes series-arm resonators S11 to S16 and parallel-arm resonators P11 to P13. Also in the ladder filter as the transmission filter, at least one of the series-arm resonators S11 to S16 and the parallel-arm resonators P11 to P13 may also be configured by an elastic wave device (for example, the elastic wave device 1) configured according to the present invention. Therefore, the occurrence of cracking of the piezoelectric film 72 can be effectively reduced or prevented.

Further, the above-described breakage of the piezoelectric film 72 easily occurs at the peripheral edge of the composite filter 71 (i.e., in the cavity portion in the vicinity of the peripheral edge of the composite filter chip). Therefore, in fig. 13, the elastic wave device of the present preferred embodiment is effectively applied to, for example, the parallel arm resonator P11, the series arm resonator S11, the parallel arm resonator P13, and the like including the cavity portion in the vicinity of the outer peripheral edge when the composite filter device 71 is viewed in plan view.

(eighth preferred embodiment)

Fig. 15 is a partially cutaway perspective view for explaining an elastic wave device according to an eighth preferred embodiment of the present invention, and fig. 16 is a plan view thereof.

The elastic wave device 81 includes a support substrate 82. The support substrate 82 includes a recess that opens to the upper surface. The piezoelectric film 83 is laminated on the support substrate 82. Thus, the cavity portion 9 is provided. The IDT electrode 84 is provided on the piezoelectric film 83 above the cavity portion 9.

Reflectors

85 and 86 are provided on both sides of the IDT electrode 84 in the direction of propagation of the elastic wave. In fig. 15 and 16, the outer peripheral edge of the cavity portion 9 is shown by a broken line. Here, the IDT electrode 84 includes first and

second bus bars

84a and 84b, a plurality of first electrode fingers 84c, and a plurality of second electrode fingers 84d. The plurality of first electrode fingers 84c are connected to the first bus bar 84a. The plurality of second electrode fingers 84d are connected to the second bus bar 84b. The plurality of first electrode fingers 84c and the plurality of second electrode fingers 84d are interleaved with each other.

In the acoustic wave device 81, a lamb wave, which is a plate wave, is excited by applying an AC electric field to the IDT electrode 84 above the cavity. Since the

reflectors

85 and 86 are disposed at both sides, resonance characteristics due to lamb waves can be obtained.

Also in the acoustic wave device 81, the corners of the first bus bar 84a and the second bus bar 84b that are located outside in the direction orthogonal or substantially orthogonal to the acoustic wave propagation direction are also located outside the cavity 9. That is, the

reflectors

85 and 86 are not positioned outside the cavity 9, but the corners of the first bus bar 84a and the second bus bar 84b of the IDT electrode 84 are positioned outside the cavity 9. Therefore, the stress concentration of the piezoelectric film 83 at these corners can be reduced, and cracking can be reduced or prevented.

As described above, the elastic wave device of the present preferred embodiment can use plate waves.

(ninth preferred embodiment)

Fig. 17 is a schematic plan view for explaining a main portion of an elastic wave device 91 according to a ninth preferred embodiment of the present invention. The elastic wave device 91 corresponds to a modified example of the elastic wave device 81. Here, the first bus bar 84a on the hot side of the IDT electrode 84 is configured in the same or substantially the same manner as the elastic wave device 81. However, the second bus bar on the ground potential side of the IDT electrode 84 is integrated with the bus bars of the

reflectors

85 and 86 to define a common bus bar. Both ends of the second bus bar 92 in the longitudinal direction extend to the outside of the cavity 9. Therefore, when viewed in plan, all of the four corners of the second bus bar 92 are located outside the cavity portion 9. Therefore, the stress concentration of the piezoelectric film 83 at all the corners of the second bus bar 92 on the ground potential side can be reduced. Therefore, the piezoelectric film 83 is less likely to be broken.

(tenth preferred embodiment)

Fig. 18 is a front sectional view for explaining an elastic wave device according to a tenth preferred embodiment of the present invention. In fig. 18, a portion similar to that in fig. 2 showing the elastic wave device 1 of the first preferred embodiment is shown.

In the elastic wave device 91, the support member 8A includes a recess 8b that opens to the upper surface. The recess 8b is closed by the piezoelectric film 2 to define a cavity portion 9. As described above, the cavity portion 9 may have a structure including a bottom. In other structures, the elastic wave device 91 is configured in the same or substantially the same manner as the elastic wave device 1.

(eleventh preferred embodiment)

Fig. 19 is a front sectional view for explaining an elastic wave device according to an eleventh preferred embodiment of the present invention. In fig. 19, a portion similar to that in fig. 2 showing the elastic wave device 1 of the first preferred embodiment is shown.

In the elastic wave device 95, the piezoelectric film 2 and the insulator 7 include the opening 2d and the opening 7b. Thus, the chamber portion 9 communicates with the bottom portion.

The other structure of the elastic wave device 95 is the same as or similar to the structure of the elastic wave device 91 shown in fig. 18. In this way, the cavity portion 9 can communicate with the outside through the opening 2d and the opening 7b, the opening 2d and the opening 7b being interposed between the cavity portion 9 and the outside.

Although preferred embodiments of the present invention have been described above, it should be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the invention is, therefore, indicated by the appended claims.

[ description of reference numerals ]

1. 21, 31, 41, 51, 61, 81, 91, 95 elastic wave device

2. Piezoelectric film

2a, 2b first and second main surfaces

2d opening

3. 4 first and second electrode fingers

5. 6 first bus bar and second bus bar

5a, 5b, 6a, 6b Long side

Short sides of 5c, 5d, 6c, 6d

5e to 5h, 6e to 6h corner

5i, 5j, 6i, 6j hypotenuse

7. Insulating layer

7a opening part

7b opening

8. 8A supporting member

8a opening part

8b concave part

9. Cavity part

23. 24 second layer electrode pattern

23a, 24a exterior

52. Protective film

71. Composite filter device

72. Piezoelectric film

73. Common terminal

74. Receiving terminal

76. Ladder filter

77. Vertical coupling resonator type filter

79. Transmitting terminal

82. Supporting substrate

83. Piezoelectric film

84 IDT electrode

84a, 84b first and second bus bars

84c, 84d first and second electrode fingers

Corner portions 84e to 84h

85. 86 reflector

110IDT electrode

111. 112 first and second bus bars

113. 114 first and second electrode fingers

115. Piezoelectric film

201. Piezoelectric film

201a, 201b first and second major surfaces

451. 452 first and second zones

Series arm resonator of S1, S2, S11 to S16

P1, P2, P11 to P13 parallel arm resonators.

Claims

1. An elastic wave device comprising:

a support substrate including a first main surface and a recess at the first main surface;

a piezoelectric film made of lithium niobate or lithium tantalate laminated on the first main surface of the support substrate and defining a cavity portion together with the recess portion; and

an electrode on the piezoelectric film and including a first bus bar and a second bus bar, a first electrode finger connected to the first bus bar, and a second electrode finger connected to the second bus bar; wherein,

the first and second bus bars include a plurality of corner portions when viewed in a plan view;

the elastic wave device is configured to use a bulk wave of a thickness slip mode; and is provided with

At least one of the plurality of corners of the first and second bus bars is outside the cavity when viewed in plan.

2. An elastic wave device comprising:

a support substrate including a first main surface and a recess opening to the first main surface;

a piezoelectric film made of lithium niobate or lithium tantalate laminated on the first main surface of the support substrate and defining a cavity portion together with the recess and the support substrate; and

when the thickness of the piezoelectric film is d and the distance between the center of the first electrode finger and the center of the second electrode finger is p, d/p is about 0.5 or less; and is

3. An elastic wave device comprising:

a piezoelectric film laminated on the first main surface of the support substrate and defining a cavity portion together with the recess portion; and

an IDT electrode located on the piezoelectric film such that a portion of the IDT electrode overlaps the cavity section; wherein,

the IDT electrode includes a first bus bar and a second bus bar, a plurality of first electrode fingers connected to the first bus bar, and a plurality of second electrode fingers connected to the second bus bar;

the plurality of first electrode fingers and the plurality of second electrode fingers are interleaved with each other;

the first and second bus bars include a plurality of corner portions when viewed in a plan view; and is

4. The elastic wave device according to any one of claims 1 to 3, wherein the at least one of the corner portions includes a corner portion located on a side face of the respective first and second bus bars at which the plurality of first electrode fingers and the plurality of second electrode fingers are connected.

5. The elastic wave device according to any one of claims 1 to 4, wherein all of the plurality of corners of the first busbar and the second busbar are outside the cavity when viewed in a plan view.

6. The elastic wave device according to any one of claims 1 to 5, further comprising:

a second layer electrode pattern laminated on at least a portion of the first bus bar and the second bus bar; wherein,

the second layer electrode pattern includes a plurality of corners when viewed in a plan view, and at least one of the plurality of corners of the second layer electrode pattern is outside the cavity portion.

7. The elastic wave device of claim 6, wherein all of the plurality of corners of the second layer electrode pattern are outside the cavity when viewed in top plan view.

8. The elastic wave device according to any one of claims 1 to 7, wherein an outer edge of at least one of the plurality of corners of the first busbar and the second busbar is curved.

9. The elastic wave device according to claim 6 or 7, wherein an outer edge of at least one corner of the plurality of corners of the second layer electrode pattern is curved.

10. The elastic wave device according to any one of claims 1 to 9,

the first bus bar and the second bus bar have a rectangular or substantially rectangular shape having a length direction;

the length direction is a direction in which the first electrode fingers and the second electrode fingers face each other, and

the plurality of corner portions of the first busbar and the second busbar include a corner portion outside one end side of the cavity portion and a corner portion outside the other end side of the cavity portion in the longitudinal direction.

11. The elastic wave device according to any one of claims 6, 7, or 9,

the second layer electrode pattern has a rectangular or substantially rectangular shape having a length direction,

the length direction is a direction in which the first electrode fingers and the second electrode fingers face each other; and is

The plurality of corner portions of the second-layer electrode pattern include corner portions outside one end side of the cavity portion and corner portions outside the other end side of the cavity portion in the longitudinal direction.

12. The elastic wave device according to claim 1 or 2,

the electrode including the first bus bar and the second bus bar, the first electrode finger, and the second electrode finger is an IDT electrode; and is

The first bus bar and the second bus bar are bus bars in the IDT electrode.

13. The elastic wave device of claim 12, wherein the elastic wave device does not comprise a reflector.

14. The elastic wave device according to claim 3, wherein the elastic wave device uses plate waves.

15. The elastic wave device according to claim 4 or 14, further comprising reflectors on both sides of an elastic wave propagation direction of the IDT electrode.

16. A ladder filter comprising:

a series arm resonator and a parallel arm resonator; wherein,

at least one of the series-arm resonator and the parallel-arm resonator is the elastic wave device according to any one of claims 1 to 14.